1. Technical Field
The present invention relates to a binder resin for an electrostatic image developing toner which is used when an electrostatic latent image formed by an electro-photographic process, an electrostatic recording process or the like is developed with a developer, and also relates to an electrostatic image developing toner produced by kneading and pulverizing the binder resin. Furthermore, the present invention relates to a binder resin liquid dispersion for an electrostatic image developing toner, produced from the binder resin, and an electrostatic image developing toner produced by using the binder resin liquid dispersion. In addition, the present invention relates to an electrostatic image developer using the electrostatic image developing toner, and an image forming method.
2. Related Art
With rapid spread of digitization technology, high image quality is recently demanded for the output such as print and copy by users at the home or office or in the publishing field. Meanwhile, demands for low energy and energy saving in corporate activities and activity result products are increasing so as to realize a sustainable society. To keep up with this trend, also in the image forming method of forming an image, for example, by an electrophotographic process or an electrostatic recording process, there is required electric power saving in the fixing step which involves a large energy consumption, or implementation of an activity with a low environmental load in the step of producing a product by using the obtained material. Examples of the countermeasure for the former include more reduction in the toner fixing temperature. When the toner fixing temperature is lowered, in addition to power saving, the waiting time until the fixing member surface reaches the fixing possible temperature after turning on the power source, so-called warm-up time, can be shortened and the life of the fixing member can be prolonged.
Incidentally, as for the binder resin of a toner, a vinyl-based polymer has been heretofore widely used and for obtaining a fixing property in high temperature, use of a polymer having a high molecular weight has been proposed. However, a vinyl-based polymer having a high molecular weight has a high softening temperature and the heat roller must be set to a high temperature so as to obtain a fixed image with excellent glossiness, but this results in reverse movement against energy saving. Furthermore, a toner using a vinyl-based polymer is liable to be attacked by the plasticizer of a plasticized vinyl chloride and has a problem that on coming into contact with the plasticizer, the toner itself is plasticized to bear tackiness and contaminate the plasticized vinyl chloride product (hereinafter referred to as a “vinyl chloride resistance property”).
On the other hand, a polyester resin has an excellent vinyl chloride resistance property, and a polyester resin having a low molecular weight can be relatively easily produced. Furthermore, a toner having blended therein a polyester resin as the binder resin is advantageous in that the toner when melted exhibits good wetting to a support such as transfer paper as compared with a toner having blended therein a vinyl-based polymer as the binder resin, and the fixing can be satisfactorily performed at a lower temperature as compared with a case using a vinyl-based polymer having a nearly equal softening temperature. Therefore, a polyester resin is being used as the binder resin for an energy-saving toner in many cases.
As for the polyester binder resin, an amorphous polyester resin obtained by polycondensing mainly an aromatic polyvalent carboxylic acid (e.g., terephthalic acid, isophthalic acid), an aliphatic unsaturated carboxylic acid (e.g., fumaric acid, maleic acid), a diol having a bisphenol structure, and an alicyclic dial (e.g., aliphatic diol, cyclohexanedimethanol) has been heretofore used, and a large number of patents have been proposed thereon. Furthermore, studies are being made also on an alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid.
The above-described resins all are usually produced by a production process requiring a high energy. In a general polycondensation process, a reaction over 10 hours or more with stirring by a great power under highly reduced pressure at a high temperature exceeding 200° C. is necessary and a large energy consumption is incurred. Accordingly, a huge facility investment is required in many cases so as to obtain durability of the reaction facility.
In the case of producing a toner by using an amorphous polyester resin, a bisphenol A derivative is widely used as the alcohol monomer of the polyester. However, since this resin is also produced by using a metal catalyst, a metal is taken into the resin and when the toner is used in a severe environment such as high-temperature high-humidity condition, the charged amount decreases due to leakage of electric charge and fogging is readily generated in the non-image area.
On the other hand, higher function, particularly, higher-speed printing is demanded in an electrophotographic printer or copying machine, and even a print image printed under severe conditions is similarly required to satisfy not only the image storability under severe conditions, for example, at a high temperature for a long time, but also the image strength such as abrasion resistance and rubbing resistance.
A toner produced by using a bisphenol A derivative as the alcohol monomer of the polyester resin may satisfy the above-described requirements when used in a normal environment, but sufficient rigidity as a resin is not yet ensured in a severe environment such as high-temperature high-humidity condition and therefore, the mechanical strength as a toner powder or the image strength as a printed matter is still insufficient, for example, thinning or offset of an image due to strong friction is readily generated also in a printed matter from a toner produced by using the resin.